Identification cards are commonly used for personal identification or security access applications. For example, an individual may require his or her own personal identification card to gain access into a secured area such as an office building, an elevator floor, an office suite, or a parking complex. To gain access to the secured area, the individual simply places the personal identification card near a reader positioned at the entrance to the secured area so that the reader, which may be networked to a remote host computer, can identify the individual and authorize access to the secured area if appropriate.
Access control systems generally include a reader and at least one transponder embedded in a portable substrate, which is typically in the form of a plastic identification card. The identification card is carried by a person to be identified or otherwise characterized by a reader of the access control system. Communication between the reader and the identification card is enabled by cooperative resonant circuits, which are provided in each reader and identification card. Each resonant circuit includes an inductor, typically in the form of an antenna, which magnetically couples to the inductor of the other resonant circuit through mutual inductance.
Communication is initiated when the identification card is proximally positioned relative to the reader. The reader has a power supply which conveys a current to the reader resonant circuit causing the reader antenna to produce an excitation signal in the form of an electromagnetic field. The excitation signal couples to the antenna of the proximally-positioned identification card through mutual inductance, and the excitation signal powers and clocks the card circuitry initiating operation of the identification card.
The identification card generates a response signal at a specified frequency and transmits the response signal back to the reader. In particular, the card resonant circuit receives a current in response to the excitation signal which causes the card antenna to produce a response signal in the form of an electromagnetic field. The response signal couples to the reader antenna through mutual inductance in substantially the same manner as described above with respect to coupling of the excitation signal to the card antenna. The identification card typically employs frequency or amplitude modulation of the response signal to encode data stored in the memory of the card circuitry into the response signal. When the response signal couples to the reader antenna, a corresponding current is induced in the reader antenna at the specified frequency. The reader processes the induced current to read the data encoded in the response signal from the identification card.
Because identification cards typically contain private and/or confidential information, there is a concern that the information can be accessed by any card reader within the path of the card holder. Current access control systems allow anyone within the range specified by the proximity card reader to excite the field and copy the access control data, thus allowing them to gain unapproved access to a supposedly secure access point. Someone looking to intercept access card information from the identification card held on a person or in their carrying bag could accomplish this with an interceptor device, such as a custom portable proximity card reader. This interception device could be placed next to the person long enough to gain critical access card information transmitted from the proximity card.
Therefore, what is needed in the art is a device and method for controlling the activation of the proximity card to prevent unauthorized interception of the access card information.